The aims of the proposal are to study adolescent males who are candidates for androgen replacement therapy to: 1. Characterize the time course of elevation of biochemical markers of bone mineral metabolism following the adminstration of testosterone and with respect to achieved serum concentrations of testosterone(T) and estradiol(E2). and 2. Determine the difference between intermittent and more consistent exposure to pubertal sex steroid levels on rates of bone turnover.